Sometimes when using loop and merge, branching, etc. there will be an error with the back button or the back button may become disabled when navigating between blocks. See the Qualtrics content on
loop and merge. Qualtrics does provide a warning on their loop and merge content page: "You cannot use Loop & Merge to go backwards in the survey. You can only use it to go forward in the survey, or repeat a block over and over."
One option you might want to consider is providing a
Table of Contents which will allow your respondents to jump around in your survey - which I am guessing you are trying to allow respondents to do?
@C_Bohn thanks for your reply. Yes, I am using a table of contents already.